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Abstract:

In a magnetic reading/writing device, a controller derives at each radius
of a recording medium a slope of a curve of track-averaged write
performance with respect to an adjustment parameter, and determines a
first set of fitting coefficients of a first equation approximating the
derived slopes in terms of a first variable representing each radius. The
controller acquires write performance dependence on a variable
representing each of multiple circumferential positions of the medium by
measuring track average write performance with respect to the
circumferential positions, and determines a second set of fitting
coefficients to approximate by a periodic function the acquired
dependence in terms of the first variable. The controller corrects a
condition value representing the adjustment parameter by subtracting from
the condition value an adjustment value obtained from functions
calculated with the first and second sets of fitting coefficients.

Claims:

1. A magnetic reading and writing device, comprising: a magnetic head
that performs a magnetic reading/writing upon a magnetic recording medium
and a flying height control; a controller that acquires dependence of
write performance of the magnetic head on a variable representing each of
a plurality of circumferential positions of the head with respect to the
medium by measuring track write performance with respect to the plurality
of circumferential positions, and derives a set of fitting coefficients
therefrom; and a head flying height control power supply that adjusts an
adjustment parameter to control the flying height of the magnetic head
according to the circumferential position based upon the set of fitting
coefficients.

2. The magnetic reading and writing device according to claim 1, wherein
the set of fitting coefficients is a set of fitting coefficients of an
equation comprising a periodic function that approximates a relation
between write performance and the variable.

3. The magnetic reading and writing device according to claim 2, wherein
the set of fitting coefficients is a function of a radial position of the
magnetic recording medium.

4. The magnetic reading and writing device according to claim 3, wherein
the function is a polynomial equation.

5. The magnetic reading and writing device according to claim 4, wherein
the degree of the polynomial equation is smaller than or equal to 5.

6. A magnetic reading and writing device, comprising: a magnetic head
that performs a magnetic reading/writing upon a magnetic recording medium
and a flying height control; a controller that acquires dependence of
write performance of the magnetic head on a variable representing each of
a plurality of circumferential positions of the head with respect to the
medium by measuring track write performance with respect to the plurality
of circumferential positions, and derives a set of fitting coefficients
therefrom; and a recording signal generation device that adjusts an
adjustment parameter to control a write current of the magnetic head
according to the circumferential position based upon the set of fitting
coefficients.

7. The magnetic reading and writing device according to claim 6, wherein
the set of fitting coefficients is a set of fitting coefficients of an
equation comprising a periodic function that approximates a relation
between write performance and the variable.

8. The magnetic reading and writing device according to claim 7, wherein
the set of fitting coefficients is a function of a radial position of the
magnetic recording medium.

9. The magnetic reading and writing device according to claim 8, wherein
the function is a polynomial equation.

10. The magnetic reading and writing device according to claim 9, wherein
the degree of the polynomial equation is smaller than or equal to 5.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of application Ser. No.
13/271,176, filed Oct. 11, 2011, and claims priority under 35 U.S.C.
§119 from Japanese Patent Application 2011-001336, filed Jan. 6,
2011, the entirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a magnetic reading and writing device and
a controller of the device.

[0004] 2. Description of the Related Art

[0005] In current hard disk drives, in order to raise recording densities
to the extent possible and realize large recording capacities for
specific combinations of magnetic reading and writing heads and a
magnetic recording medium, processing has been performed to optimize the
recording current and track density, as well as the heater power for
control of the flying height of the magnetic reading and writing heads.
Optimum conditions differ depending on the radius, due to the
circumferential speed dependence and skew dependence of the head flying
characteristics, as well as the radial dependence of the magnetic
characteristics of the magnetic recording medium. Hence, in general,
optimization processing depending on the radius has been performed in a
magnetic recording system. Specifically, the write current, distance
between tracks (hereafter called the "track pitch"), linear recording
density, as well as the heater power for the flying height control are
selected so as to maximize the recording density at each radius, as a
result of which drive storage capacity is optimized.

[0006] Japanese Patent Application Laid-open No. H8-45007 discloses a
magnetic disk device which performs correction of writing signals and
reproduced waveforms is disclosed. In the magnetic disk device, when data
is received from a higher-level device during operation, a recording
system converts the data into recording signals and outputs the signals
to the magnetic head, thereby recording the recording signals on the
magnetic disk. At this time, a preshifter performs correction such as
delaying the recording signals. The correction amount in this case is
calculated by recording correction amount calculation means based on the
peak position of a reproduced waveform. On the other hand, a reading
system of the device converts readout waveforms read by the magnetic head
from the magnetic disk into data, and outputs the data to a higher-level
device. At this time, the filter corrects the amplitude and similar of
the readout waveforms. The correction amount in this case is calculated
by read/write correction amount calculation means, based on the pulse
width of the readout waveforms (see paragraphs

[0008] and

[0009] of
Japanese Patent Application Laid-open No. H8-45007). In accordance with
this device, by calculating a correction amount in advance for each
track, the correction amount which absorbs scattering at the time of
magnetic disk manufacture and the like can be calculated (see paragraphs

[0021],

[0026] and[0027], and similar of Japanese Patent Application
Laid-open No. H8-45007).

[0007] Further, Japanese Patent Application Laid-open No. 2009-129532
discloses a mechanism which, in order to compensate readout signal
output, uses a heater for control of the flying height of a magnetic
read/write head.

[0008] In an actual magnetic recording medium, there are cases in which
there is a gentle characteristic distribution not only in the radial
direction, but in the circumferential direction as well. If reading and
writing optimization processing is performed using such a magnetic
recording medium with a dependence only on the radial direction, as in
the prior art, then it is possible that the recording capacity will be
greatly inferior to what should in principle be obtained when performing
optimization which includes a dependence on the circumferential position
as well. In particular, where the write performance is concerned, when
there is unevenness in the circumferential position, under constant
conditions in the circumferential position, the write width is broad in
portions where the write performance is high and the track pitch cannot
be narrowed. Conversely, in portions where the write performance is low,
under conditions optimized for portions with high write performance,
there is the concern that write performance will be inadequate.

SUMMARY OF THE INVENTION

[0009] This invention was devised in light of the above problems, and has
as an object the provision of a magnetic reading and writing device which
can perform reading and writing optimization processing which depends on
the circumferential position as well, without requiring the addition of
considerable resources compared with conventional optimization methods.

[0010] In order to attain the above object, a first mode of the invention
is a magnetic reading and writing device, which includes a magnetic head,
a magnetic recording medium, nonvolatile memory, and a controller. The
magnetic head has a magnetic read/write function and a flying height
control function. On and from the magnetic recording medium, reading and
writing are performed by the magnetic head. The nonvolatile memory stores
a write current, a track pitch, a linear recording density and a flying
height control heater power, selected such that the recording density is
maximum at each radius of the magnetic recording medium. The controller
as a first optimization means, derives, taking the write current or the
flying height control heater power as a write performance adjustment
parameter, a slope of a track average write performance with respect to
the write performance adjustment parameter at each of a plurality of
radii of the magnetic recording medium. The controller also stores in the
nonvolatile memory a first set of fitting coefficients for a case in
which the slope is approximated by a polynomial equation for the radius
of the magnetic recording medium. The controller, as a second
optimization means, acquires the circumferential position dependence of
the write performance at each of the plurality of radii of the magnetic
recording medium, using the write current, the track pitch, the linear
recording density and the flying height control heater power stored in
the nonvolatile memory. The controller stores in the nonvolatile memory a
second set of fitting coefficients obtained by approximating the
circumferential position dependence by a periodic function. The
controller, as a correction means, uses a track-averaged write
performance change rate which is a function of the radius and is
calculated using the first set of fitting coefficients, and a local write
performance function which is a function of the radius and
circumferential position and is calculated using the second set of
fitting coefficients, to correct the write performance adjustment
parameter at each of the radii and in each of circumferential positions
by subtracting a value of (local write performance
function-track-averaged write performance)/track-averaged write
performance change rate.

[0011] Further, a second mode of the invention is characterized in that,
in the first mode, the write performance adjustment parameter is the
write current.

[0012] Further, a third mode of the invention is characterized in that, in
the first mode, the write performance adjustment parameter is the flying
height control heater power.

[0013] Further, a fourth mode of the invention is characterized in that,
in any one of the first through third modes, the degree of the radius r
of the track-averaged write performance change rate is 3 or higher and 5
or lower.

[0014] By means of this invention, a magnetic reading and writing device
can be provided with a local write performance function to correct the
write performance adjustment parameter (the write current or the flying
height control heater power). The local write performance function is a
function of the radius and the circumferential position obtained by
approximating the circumferential position dependence of the write
performance of a magnetic head for a magnetic recording medium. By this
means, reading and writing optimization processing which also depends on
the circumferential position can be performed, without requiring the
addition of considerable resources compared with conventional
optimization methods.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows the magnetic reading and writing device of one
embodiment of the invention;

[0016]FIG. 2 shows a controller of the magnetic reading and writing
device according to one embodiment of the invention;

[0017]FIG. 3 shows a flying height control heater power dependence of
overwriting;

[0018]FIG. 4 shows a circumferential position distribution of overwriting
(prior to adjustment of the flying height control heater power by
circumferential position);

[0019]FIG. 5 shows a circumferential position distribution of the center
track remaining signal intensity for adjacent track erasure (prior to
adjustment of the flying height control heater power by circumferential
position);

[0020]FIG. 6 shows a circumferential position distribution of overwriting
(after adjustment of the flying height control heater power by
circumferential position); and

[0021] FIG. 7 shows a circumferential position distribution of the center
track remaining signal intensity for adjacent track erasure (after
adjustment of the flying height control heater power by circumferential
position).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Below, embodiments of the invention are explained in detail
referring to the drawings.

[0023]FIG. 1 shows the magnetic reading and writing device of one
embodiment of the invention. A controller 1 controls a rotor 12 connected
to a magnetic recording medium 6, issues reading and writing instructions
to a code conversion/signal analysis device 3, exchanges data with an
external interface, and similar, and in addition handles optimization
processing for the combination of a magnetic head 11 and the magnetic
recording medium 6. Further, instructions to a head flying height control
power supply 9 are output according to a read/write position. In
nonvolatile memory 2, various types of information, including fitting
coefficients described below, are held. Examples of non-volatile memory
include read-only memory, flash memory, ferroelectric RAM, most types of
magnetic computer storage devices (e.g. hard disks, floppy disks, and
magnetic tape), optical discs.

[0024] The controller 1 may be a general purpose computer or a dedicated
special purpose hardware item, and the optimization processing may be
performed by hard-wired logics or software/firmware stored in a memory.
FIG. 2 shows one example configuration of the controller 1. The
controller 1 may include a bus 130 or other communication mechanism for
communicating information and a processor 150 coupled with the bus 130
for processing the information. The controller 1 also may include a main
memory 110, such as a random access memory (RAM) or other dynamic storage
device (e.g., dynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM
(SDRAM), flash RAM), coupled to bus for storing information and
instructions to be executed by the processor 150. In addition, main
memory 110 may be used for storing temporary variables or other
intermediate information during execution of instructions to be executed
by processor. A storage device 120, such as a magnetic disk or optical
disk, may be provided and coupled to the bus 130 for storing information
and instructions. This storage device is an example of a computer
readable medium, upon which the program may be encoded. The controller 1
also may include input/output ports 140 to input signals to couple the
controller 1. Such coupling may include direct electrical connections,
wireless connections, networked connections, etc., for implementing
automatic control functions, remote control functions, etc. Suitable
interface cards may be installed to provide the necessary functions and
signal levels. The controller 1 also may include a communication
interface 160 coupled to the bus 130. The communication interface 160 may
provide a two-way data communication coupling to a communication link 180
that may be connected to, for example, an external device 20.

[0025] The magnetic head 11 has a flying height control heater (not
shown), recording head 5, and a reading element 7. The radial position of
the magnetic head 11 is set by the magnetic head position locator 10
according to an instruction issued by the controller 1. The magnetic head
position locator 10 drives a voice-coil rotator of a magnetic head
assembly (not shown) and locates the magnetic head 11 in a right radial
position.

[0026] A recording signal generation device 4 transmits signals for
recording to the recording head 5 based on instructions from the code
conversion/signal analysis device 3, and the recording head 5 performs
magnetic recording on the magnetic recording medium 6. Information
recorded on the magnetic recording medium 6 is captured as signals via
the reading element 7. The captured signal, after passing through a
signal amplifier 8, is sent to the code conversion/signal analysis device
3, where the recorded information is restored and is sent to the
controller 1.

[0027] Below, the operation of the magnetic reading and writing device of
this embodiment is explained. In optimization processing, the controller
1 performs various processing; at this time, the controller 1 can be
viewed as means for executing the various processing.

[0028] First, as in conventional optimization methods, the controller 1
performs optimization of the track pitch, linear recording density, write
current, and flying height control heater power, with dependence only on
the radial direction (step 101). By this means, the physical format is
decided. The various values obtained by optimization are stored in the
nonvolatile memory 2.

[0029] Next, at a plurality of radii, the track-averaged write performance
is derived, when the flying height control heater power during writing is
shifted, taking as the center the flying height control heater power
decided by optimization in step 101 (step 102). This flying height
control heater power is a parameter for adjusting the write performance,
and is called the "write performance adjustment parameter". FIG. 3 shows
an example of measurement for perpendicular magnetic recording. The
horizontal axis indicates the flying height control heater power during
writing, centered on the flying height control heater power (mW) obtained
by optimization depending only on the radial direction, and the vertical
axis indicates, as a write performance evaluation value, the "overwrite",
defined as the ratio of the remaining intensity of a high-density
recorded signal to the initial recorded signal intensity when low-density
recording is performed after high-density recording.

[0030] The relation of FIG. 3 was fit to a first-degree equation, and the
slope Δf/Δp of the overwrite to the flying height control
heater power p during writing was derived (step 103). This was performed
at each radius, and fitting coefficients when approximating the slope
Δf/Δp with respect to the radius r by a polynomial equation
were determined (step 104). These values were stored in nonvolatile
memory 2. These fitting coefficients (corresponding to the "first set of
fitting coefficients") can be used at radius r to calculate the
track-averaged write performance change rate (Δf/Δp)(r).

[0031] Next, at a plurality of radii, the optimization conditions of step
101 for each radius are used to acquire the circumferential position
dependence of the overwrite (step 105). The solid line in FIG. 4
indicates an example for a certain radius. Here, the horizontal axis
indicates each of the directions when an entire circumference is divided
into N=32 parts, and the vertical axis indicates the overwrite calculated
only for that direction.

[0032] Further, this circumferential position dependence of the overwrite
is fit to a periodic function, with one rotation as one period (step
106). That is, when the jth circumferential position overwrite
measurement results is f(j), this f(j) is approximated by

f(j)=a(0)/2+Σ'a(k)cos(2πjk/N)+Σ'b(k)sin(2πjk/N) (1).

[0033] Here Σ' is the sum for values of k starting from 1. It is
assumed that a(k)=(2/N)Σf(j)cos(2πjk/N) and
b(k)=(2/N)Σf(j)sin(2πkj/N). Here Σ is the sum for values
of j from 0 to N-1.

[0034] The broken line in FIG. 4 represents the result of approximation
using seven parameters from a(0) to a(3) and b(1) to b(3).

[0035] The above-described measurement and fitting are performed for a
plurality of radii. Fitting coefficients a(k), b(k) at radius r=r(i) are
denoted by a(i, k) and b(i, k) respectively. The fitting coefficients
when the relation between these coefficients a(i, k) and b(i, k) to
r=r(i) is approximated by a polynomial equation with respect to the
radius r (corresponding to the "second set of fitting coefficients") are
determined (step 107). These values are stored in the nonvolatile memory
2. On the basis of the stored fitting coefficients, functions a(r, k) and
b(r, k) of the radius r are obtained.

[0036] Finally, shifts Δf(r, j) from the track averages at radius r
and circumferential position j of the local write performance function
f(r, j) expressing the local write performance is calculated, removing
the constant term in equation (1):

Δf(r, j)=Σ'a(r, k)cos(2πkj/N)+Σ'b(r,
k)sin(2πkj/N) (2)

(step 108).

[0037] The heater power p(r) optimized in the radial direction is modified
to obtain the heater power for a direction j, p(r, j):

p(r, j)=p(r)-Δf(r, j)/(Δf/Δp)(r) (3)

and actual recording is performed (step 109).

[0038] The radial-direction distribution is normally gentle, and so it is
desirable that the degree of the polynomial approximation not be made too
high. For example, from 3 to 5 degrees or so is desirable. The number of
samplings exceeding (the number of polynomial equation degrees+1) is
sufficient.

[0039] Further, each of the above-described processing can be performed in
any order, so long as ultimately the heater power p(r, j) can be
corrected.

[0040] In the above explanation, the flying height control heater power
during writing was used as the write performance adjustment parameter;
but the write current may be used. With respect to minute changes,
increasing the flying height control heater power and increasing the
write current induce similar actions. That is, there is the tradeoff that
as the write performance is increased (and consequently the linear
recording densities is raised), the write width increases (the track
pitch worsens), and so the recording density is raised by performing
optimization which includes a dependence on the circumferential position,
as described below.

[0041] In optimization by this method, high recording densities can be
realized as follows. In the magnetic reading and writing device shown in
FIG. 1, FIG. 5 shows the results of measurement of the circumferential
position dependence of the remaining signal intensity at the original
track center, when a rectangular wave was recorded on a track sector, and
erasure was then performed at a position distant by the track pitch from
the track center. If this value cannot be maintained at a fixed value or
higher (generally approximately 80%), the signal recorded on the original
track cannot be correctly reproduced as a result of recording on the
adjacent track.

[0042]FIG. 6 and FIG. 7 respectively show the circumferential position
dependence of the overwrite and the circumferential position dependence
of the remaining signal intensity upon adjacent track erasure, upon
performing heater power adjustment during writing by angle according to
equation (3). Specifically, the flying height control heater power at
each circumferential position was set, relative to the heater setting
prior to adjustment, to a value reduced by

(overwrite measured value at the circumferential
position-circumferential position average value of overwrite)/1.6.

[0043] By means of the control indicated by equation (3), the
circumferential position dependence not only of overwrite, but also of
remaining signal intensity upon adjacent track erase is also reduced. In
FIG. 7, the solid line represents measurements at the track pitch,
obtained as the result using the conventional optimization method of step
101, and the broken line represents measurements with the track pitch
reduced to 95%. The broken line of FIG. 7 and the minimum values in FIG.
5 substantially coincide; this fact indicates that by means of the
control of equation (3), 5% reduction of the track pitch (an increase by
5% in the track density) is possible.

[0044] In this method, in addition to the optimization by radius of the
prior art, control based on the angle, as well as storage capacity for
this control, are necessary; but the data to be stored is only fitting
coefficients, requiring very little data storage, and no addition of
considerable resources over those used in conventional optimization
methods is required.

[0045] As described above, by adopting this method to perform
optimization, the margin accompanying the circumferential position
distribution of write performance can be reduced when performing
optimization, so that even when optimizing for the combination of the
same magnetic head and magnetic recording medium, higher densities can be
attained compared with conventional optimization methods.